Cold storage is an implementation of storage at a data center, and cold storage is applicable to data that needs to be saved but is rarely read. With arrival of a big data era, cold storage has gradually become a topic of great concern. Because data is rarely accessed, a performance requirement of cold storage for a storage device is not high. To reduce storage costs, for cold storage, a storage device with a large capacity, low power, and low costs may be used. For conventional cold storage, a magnetic tape library is usually used to store data. However, the magnetic tape library has a relatively high access delay. To reduce an access delay in a data reading process, in the prior art, there is a solution of implementing cold storage using a hard disk drive or solid state drive. However, this solution of implementing cold storage using a hard disk drive or solid state drive not only has high costs, but also has relatively high power.
To reduce system power, a storage device provided in the prior art includes multiple scheduling domains that work independently, and each scheduling domain includes multiple groups of hard disk drives. At any moment, only a maximum of one group of hard disk drives are allowed to spin up simultaneously or work simultaneously in a same scheduling domain. For any scheduling domain, the storage device separately schedules different disk groups according to a request queue to process service requests. For this disk group scheduling manner in the prior art, system power is reduced, but a switching time length between disk groups is introduced. The switching time length may be several seconds or even dozens of seconds. Therefore, when multiple service requests are being processed, if the service requests are alternately distributed on different disk groups, frequent switching between the disk groups is caused, and a processing delay is increased.